The present invention relates to a hydrodynamic bearing unit. This bearing unit is preferably used particularly for supporting a spindle motor in information apparatus, for example, in a magnetic disk device such as an HDD, an FDD or the like, an optical disk device such as a CD-ROM, a DVD-ROM or the like, and a magneto-optical disk device such as an MD and an MO or the like, or for supporting a spindle in a polygon scanner such as a laser beam printer (LBP) or the like.
In the spindle motor of each kind of the above information apparatus, a higher speed, a lower cost, and a lower noise are demanded in addition to the high rotation precision or the like. One of the key elements that determine these performance requirements is a bearing for supporting a spindle of the motor. In recent years, as this kind of bearing unit, the usage of the hydrodynamic bearing with excellent characteristics is investigated to meet the demanded performance, or the bearing is actually used.
In spindle motors for the above information apparatus in recent years, the high rotation precision is more strongly demanded in an attempt to increase the information recording density and obtain higher speed rotation. In order to meet this demand, still higher rotation precision is demanded with respect to the hydrodynamic bearing incorporated in the above spindle motors.
As a factor which largely affects rotation precision of hydrodynamic bearings, clearance control in a radial bearing clearance and a thrust bearing clearance for generating dynamic pressure is considered important.
The present invention aims at providing a hydrodynamic bearing unit with a high rotation precision wherein clearance control of the radial bearing clearance and the thrust bearing clearance is made appropriate.
Furthermore, an object of the present invention is to suppress the friction of a radial bearing surface and a thrust bearing surface to maintain an excellent bearing performance in the hydrodynamic bearing unit described above.